The objectives of this application are to: 1. Produce allotypic monoclonal antibodies that distinguish class I and class II antigens coded by the RT1 loci (major histocompatibility complex (MHC)) in the laboratory rat. 2. Characterize the monoclonal anti-MHC antibodies by biochemical and genetic methods to determine their antigenic specificity for class I and class II antigens of different MHC haplotypes using 11 strains of inbred rats. The antibodies will be used in combination with other procedures for genetic definition within the MHC. Phase I: Induction and Characterization of Allotypic Monoclonal Antibodies to Rat Major Histocompatibility Complex Class I and Class II Antigens Using One Donor Strain. Phase II: Production and Characterization of Monoclonal Antibodies Against the 10 Know Haplotypes of the Rat MHC. Phase III: Development of a Series of Test Kits for Typing MHC Haplotypes of Inbred Rats.